Bow tie-shaped fibers and spherical microparticles with controlled dimensions and shapes were fabricated with poly(ethylene glycol) diacrylate hydrogel utilizing hydrodynamic shear principles and a photopolymerization strategy under a microfluidic regime. Decreasing the flow rate ratio between the core and sheath fluids from 25 (50:2) to 1.25 (100:80) resulted in increasing the particles size and reducing the production rate by 357 and 86%, respectively. The width of the fibers increased by a factor of 1.4 when the flow rate ratio was reduced from 2.5 to 1 due to the decrease of the shear force at the fluid/fluid interface. The stress at break and Young's modulus of the fibers were enhanced by 32 and 63%, respectively, when the sheath-to-core flow rate ratio decreased from 100:40 to 100:80. The fiber fabrication was simulated using the finite element method, and the numerical and experimental results were in agreement. Adult hippocampal stem/progenitor cells and bone-marrow-derived multipotent mesenchymal stromal cells were seeded onto the fibrous scaffolds in vitro, and cellular adhesion, proliferation, and differentiation were investigated. Microgrooves on the fibers' surface were shown to positively affect cell adhesion when compared to flat fibers and planar controls.
Keywords: bow tie-shaped fibers; cell adhesion improvement; finite element method; hydrodynamic focusing; microfluidics; photopolymerization.